Temperature compensator units for hydraulic circuits



y 1, 1965 R. D. SMITH 3,182,458

TEMPERATURE COMPENSATOR UNITS FOR HYDRAULIC CIRCUITS Filed May 8, 1964 FIG. 7.

FIG. 2.

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RIcnARo D. Smrrn United States Patent 3,182,453 TEMPERATURE COMPENSATOR UNITS FOR HYDRAULIC CRCUITS Richard D. Smith, Market Weighton, England, assignor to Armstrong Patents Co. Limited, London, England, a British company Filed May 8, 1964, Ser. No. 366,033 Claims priority, application Great Britain, May 10, 1963, 18,508/ 63 2 Claims. (Cl. 60-545) This invention concerns temperature compensator units for hydraulic circuits.

For the correct operation of a double-acting, hydraulic remote control circuit of the type wherein actuation of a hydraulic transmitter which is connected by twin hydraulic lines to a hydraulic receiver or load-displacing member causes the latter to repeat the transmitter function, it is essential to provide the hydraulic circuit with some means for compensating for variations with temperature of the volume of hydraulic fluid in the circuit, since otherwise, during an increase in environmental temperature the pressurization of the hydraulic fluid resulting from its expansion may create a hydraulic lock, while during a temperature decrease, the reduced volume of the hydraulic fluid may permit such a degree of lost motion in the transmitter and/ or receiver units that the circuit fails or at least becomes unreliable. The invention seeks to provide a temperature compensator unit for use in such hydraulic circuits and which, by using a limited number of moving parts, will be simple in manufacture and will function reliably in operation to accommodate hydraulic fluid volume changes.

According to the present invention, a temperature compensator unit for a twin line, double-acting hydraulic remote control circuit comprises a body member having a pair of spaced, parallel hydraulic cylinders each connectable to one of the hydraulic lines of said circuit and each housing a piston slidable in said cylinder, a pillar fixedly located in said body member to extend centrally between and behind said hydraulic cylinders in a direction parallel thereto, a bridge member engaged upon and slidable along said pillar and extending symmetrically and transversely relative to said pillar and behind said pistons, said pistons acting against said bridge member, and spring means urging said bridge member towards said pistons for balancing the forces exerted on said bridge member by said pistons, a rocking clearance being provided between said pillar and said bridge member to permit the latter to lock on said pillar whenever a degree of unbalance occurs in the piston load exerted on said bridge member.

The invention will be described further, by way of example, with reference to the accompanying drawings, in Which:

FIG. 1 is a schematic illustration of a hydraulic re mote control circuit embodying a temperature compensator unit according to the invention; and

FIG. 2 is a sectional elevation of the temperature compensator unit.

A typical twin line, double-acting hydraulic remote control circuit is shown in FIG. 1, wherein a hydraulic transmitter or actuator having an operating handle 12 is connected by twin hydraulic pipelines 14, 16 to a hydraulic receiver or load-displacing unit 18 which is shown by way of example as having a load-displacing lever arm 20. Such hydraulic transmitters and receivers may take a number of dilIerent forms, but typically each has a pair of hydraulic cylinders, each of the cylinders in the transmitter 10 being connected by a line 14 or 16 to a corresponding cylinder in the receiver 18, and a piston is arranged in each cylinder with means connecting the han- 3,182,458 Patented May 11, 1965 die 12 or lever arm 20 to the respective pair of pistons, whereby movement of the handle 12 causes the transmitter pistons to execute complementary movements in their respective cylinders, setting up a corresponding displacement of hydraulic fluid in the lines 14, 16, which in turn causes the receiver pistons to repeat the movement of the transmitter pistons, and the lever arm 20 to repeat the movement imparted to the operating handle 12.

A hydraulic circuit such as shown in FIG. 1 can only operate successfully over a wide temperature range, however, if proper allowance is made for the variation with temperature of the volume of the hydraulic fluid in the circuit. For this reason, a temperature compensator unit 26 is connected into the circuit by lines 22, 24 to accommodate expansions and contractions of the fluid volume.

The temperature compensator unit 26 is shown in more detail in FIG. 2, and comprises a body member 28 having a pair of spaced, parallel hydraulic cylinders 30 in each of which is slidably received a piston 32. The forward ends of the cylinders 30 terminate in hydraulic connections 34 for the lines 22, 24. Between the cylinders, the body member 28 is formed with a relatively massive, upstanding block 36 which is centrally bored in a direction parallel with the cylinders to receive as an interference fit, an elongated pillar 38 which extends for some distance rearwardly of the body member 38 and cylinders 36. On the pillar 38 is slidably mounted a transverse bridge member in the form of a yoke bar 40 and a slight clearance is left between the pillar and yoke bar to enable the latter to rock relative to the pillar, for a purpose hereinafter to be more fully described. The yoke bar 40 is resiliently urged towards the rear or inner ends of the cylinders 30 by a helical spring 42 engaged upon the pillar 38, and at each of its end regions, a connecting rod 44 connects the yoke bar to one of the pistons 32.

In the operation of the temperature compensator unit, the hydraulic connections 34 are respectively joined by the lines 22 and 24 in parallel with the twin lines 14 and 16 of the hydraulic circuit, so that one of the cylinders 36 is in communication with one side of the circuit and the other cylinder 30 is in communication with the other side of the circuit (each side of the hydraulic circuit consisting of one of the transmitter cylinders or equivalent hydraulic compartment, the corresponding receiver cornpartment and the hydraulic line 14 or 16 joining them together). During initial setting-up, the circuit is charged with sufiicient hydraulic fluid to bring the pistons 32 to rest at the mid-position of their travel in their respective cylinders 30. A rise in temperature will then create equal expansions of the hydraulic fluid in the two sides of the circuit, resulting in the application of equal pressures to the heads of the two pistons 32, which are thus moved rearwardly in their cylinders to increase the overall volume or" the circuit and relieve the pressure rise. Conversely, if a temperature fall should occur, equal fluid contractions and equal falls of pressure will take place in the two sides of the circuit and the pistons are urged forwardly in their cylinders by the action of the spring 42 to follow up the fluid volume reduction. In this way, temperature changes are compensated while the circuit is idle.

When the transmitter 10 is actuated to place the circuit in operation, pressure is generated in one of the lines 14 or 16 and there is a tendency for a fall in pressure to occur in the other line. Since unequal pressures are thus applied to the two pistons 32, an unbalanced load results on the yoke bar 40, which then tilts or rocks out of its transverse attitude relative to the pillar 33 and locks firmly on the pillar until such time as movement of the transmitter control lever 12 ceases and fluid pressure balance in the circuit is restored. It will be appreciated that the amount of tilt or rocking motion which the yoke bar 40 must undergo in order to lock will depend upon such factors as the physical size of the temperature compensator unit and the order of hydraulic fluid pressure in the hydraulic circuit, since on the one displacement of the two pistons 32 before locking is achieved, and an undesirable degree of lost motion appears in the system. By way of example, it has been t'ound that with a pillar diameter of the order of one inch good working results are achieved with a clearance in the range 0.001 inch to 0.002 inch. It is also desirable that some care be exercised in the choice of materials for the pillar and the yoke bar, which desirably should be of a steel that is tough and resistant to distortion and to wear; however, the steel should not have too hard a surface or there is risk of adversely affecting the locking action, although naturally the surface must not be so' soft as to permitthe yoke bar to dig into the pillar.

By way of example,-one suitable steel is that known under the designation En. 36, which is a 3% nickel chromium case-hardening steel made to British Standard specification No. 970.

With a relatively small clearance between the pillar 38 and yoke bar 40, it is important that the pillar be firmly secured in the body member 28 of the unit, and this is achieved partly by the interference fit of the pillar in the bore of the block 36, and partly by the provision of a locking screw 46 inthe block and engaging a correspondingly threaded hole in the pillar to draw the latter tightly into the block. A releasable cover 48 is provided to enclose the pillar, yoke bar and piston connecting rods and is secured by a screw 50 to the opposite end of the pillar.

It will be appreciated that in situationswhere the hydraulic, receiver 18 is required to be a load-supporting rather than simply an indicating unit, a hydraulic locking valve must be arrangedin each of the lines 14 and 16 adjacent the receiver 18 in order to prevent the supported load from creating in thecircuit a pressure unbalance resulting in locking of the yoke bar 40 on the pillar 38, with consequent inability of the pistons to respond to fluid volume changes. The provision of a hydraulic locking valve adjacent the receiver unit 18 prevents this by hydraulically isolating the unit 18 from the remainder of the circuit under load-supporting conditions.

Again, although the initial'setting-up of the temperature compensator has been described assuming normal temperature conditions, situations can arise where settingup must be carried out at a known maximum or a known minimum temperature. In such cases, of course, the setting-up procedure is varied by charging the circuit with hydraulic fluid sufiicient to bring the pistons to 'Which ever extremity of their movement in their respective cyl inders is appropriate, thus allowing only for a temperature change in the opposite direction.

I claim: I

l. A hydraulic compensator unit comprising a body member formed with a pair of hydraulic ports, a pair of spaced, parallel hydraulic cylinders in said body member and each communicating with one of said ports, a piston slidable in each cylinder responsive to the appearance of hydrauliic pressure in the associated port, a pillar fixedly located in said body member to extend centrally between and behind said hydraulic cylinders in a direction parallel thereto, a bridge member engaged with rocking clearance uponand slidable along said pillar, said bridge member extending symmetrically and transversely relative to said pillar and behind said pistons, said pistons acting against said bridge member, andspring means urging said bridge member towards said pistons for balancing the forces exerted on said bridge member'by said pistons, said rocking clearance permitting said bridge member to tilt and lock upon said pillar whenever unbalance occurs in the piston load exerted on said bridge member.

2. In 'a twin line, double-acting, hydraulic remote control circuit, a fluid volume compensator unit comprising a body member having a relatively massive central block portionand formed with a pair of spaced, parallel hydraulic cylinders situated one on each side of said central block portion, means connecting eachof' said cylinders to one of the circuit lines, a piston in each cylinder, a pillar fixed in said central block portion to extend centrally between and behind said hydraulic cylinders in a direction parallel thereto, a yoke bar slidable with rocking clearance upon said pillar,'-said yoke bar extending transversely of and symmetrically relative tosaid pillar and behind said pistons, a connecting rod pivotally joining each endofsaid yoke bar to one of the pistons, and means resiliently biasing said yoke bar towards said pistons to balance the piston load created by pressure in said circuit lines, said rocking clearance permitting said yoke bar to tilt and lock onsaid pillar whenever 'said piston load becomes unbalanced.

No references cited.

JULIUS E. WEST, Primary Examiner. 

1. A HYDRAULIC COMPENSATOR UNIT COMPRISING A BODY MEMBER FORMED WITH A PAIR OF HYDRAULIC PORTS, A PAIR OF SPACED, PARALLEL HYDRAULIC CYLINDERS IN SAID BODY MEMBER AND EACH COMMUNICATING WITH ONE OF SAID PORTS, A PISTON SLIDABLE IN EACH CYLINDER RESPONSIVE TO THE APPEARANCE OF HYDRAULIC PRESSURE IN THE ASSOCIATED PORT, A PILLAR FIXEDLY LOCATED IN SAID BODY MEMBER TO EXTEND CENTRALLY BETWEEN AND BEHIND SAID HYDRAULIC CYLINDERS IN A DIRECTION PARALLEL THERETO, A BRIDGE MEMBER ENGAGED WITH ROCKING CLEARANCE UPON AND SLIDABLE ALONG SAID PILLAR, SAID BRIDGE MEMBER EXTENDING SYMMETRICALLY AND TRANSVERSELY RELATIVE TO SAID PILLAR AND BEHIND SAID PISTON, SAID PISTONS ACTING AGAINST SAID BRIDGE MEMBER, AND SPRING MEANS URGING SAID BRIDGE MEMBER TOWARDS SAID PISTONS FOR BALANCING THE FORCES EXERTED ON SAID BRIDGE MEMBER BY SAID PISTONS, SAID ROCKING CLEARANCE PERMITTING SAID BRIDGE MEMBER TO TILT AND LOCK UPON SAID PILLAR WHENEVER UNBALANCE OCCURS IN THE PISTON LOAD EXERTED ON SAID BRIDGE MEMBER. 